Referring to FIG. 1, FIG. 1 is block diagram showing a structure of a source driver 10 of a liquid display. The source driver 10 includes operational amplifiers OP1-OPn, a resistor string including resistors R1-Rn, a digital-to-analog converter 14, an output buffer and a switch circuit. The source driver 10 obtains a plurality of reference voltages VR1-VRn from a reference voltage supply (not shown), and receives the pixel values transmitted by the channels ch1-chn to convert the pixel values into the analog driving voltages, and sends in parallel the analog driving voltages on these channels to a set of corresponding data lines in accordance with scanning timing and data polarity inversion timing.
Each of the operational amplifiers OP1-OPn is used as an input buffer for each of the reference voltages VR1-VRn. After being received and outputted by the buffers, the reference voltages are divided by the resistors VR1-VRn, and thus two sets of gamma voltages with positive and negative data polarity are generated respectively. These gamma voltages are then input to the digital-to-analog converter 14. The digital-to-analog 14 may output a corresponding gamma voltage of the two sets of gamma voltages for each channel, based on the pixel value and data polarity of the channel. The voltage output by the digital-to-analog converter 14 is then output as a driving voltage via the output buffer 16. The switch circuit 18 is used to switch the connection between the output channels in conjunction with the data polarity inversion timing, so as to implement different driving modes, such as frame inversion, row inversion, column inversion, dot inversion or two dot lines inversion and the like.
However, since the operational amplifiers have inherent output voltage offsets and the inherent output voltage offsets are different from each other, the final driving voltages produced have different voltage offsets, too. Therefore, the distinct luminance or color difference occurs due to the different offsets in the driving voltages, and thus forming the so-called “band mura”.